In the treatment of various heart malfunctions, it has been found beneficial to modify the conduction paths within the heart, usually by cutting specific conduction paths, for example in the region of the A-V node or the His bundle or the ventricles. This can be accomplished surgically, but recently more preferable non-surgical techniques have been developed.
In one prior art technique, a catheter having one or more electrodes is advanced into the heart and a plate-like electrode is positioned external to the patient. A high energy d.c. voltage is applied between the electrodes causing a modification of the conduction system. Such a technique is described by J. Gallagher et al in "Catheter Technique for Closed-Chest Ablation of the Atrioventricular Conduction System," New England Journal of Medicine, Vol. 306, No. 4, Jan. 28, 1982, pp. 194-200. The d.c. shock technique causes burning of the tissue surrounding the electrode positioned in the heart and produces effects which are not at all localized.
A technique utilizing a laser catheter produces more localized effects. A catheter having an optical fiber passing through it is advanced to the desired location in the heart. Energy from an external laser is conducted by the optical fiber into the heart. This technique is described by Onkar S. Narula et al in "Microtransection of the His Bundle with Laser Radiation Through a Pervenous Catheter: Correlation of Histologic and Electrophysiologic Data," American Journal of Cardiology, July 1984, pp. 186-192. While the laser catheter technique produces localized effects, it requires complex and expensive equipment. In addition, a catheter containing an optical fiber has limited flexibility, thereby making it difficult to position the tip of the catheter in the desired location. Furthermore, a separate electrode and conductor must be provided for sensing potentials in the conduction paths. A technique for high frequency ablation of a His bundle in the heart is disclosed in U.S. Pat. No. 641,649, issued Feb. 10, 1987 to Walinsky et al. A catheter in the form of a coaxial transmission line with an antenna at its distal end is advanced into the heart in the region of the His bundle, and the potentials sensed by the catheter are measured and displayed. The catheter position is adjusted until the desired potentials are obtained. Then high frequency energy is applied to the transmission line causing ablation of portions of the His bundle. The high frequency technique produces undesirable burning of tissue surrounding the antenna, and its effects are not well localized.
A cauterizing electrode having a platinum wire loop at its tip is disclosed in U.S. Pat. No. 359,506 issued Mar. 15, 1887 to Goodwillie. Medical instruments having wire loops at their tips are also disclosed in U.S. Pat. No. 2,224,467 issued Dec. 10, 1940 to Wolf and in U.S. Pat. No. 4,643,187 issued Feb. 17, 1987 to Okada. None of these patents disclose a device which can be advanced through a blood vessel to the heart.
It is a general object of the present invention to provide methods and apparatus for non-surgical microtransection or macrotransection of desired portions of internal body organs.
It is another object of the present invention to provide methods and apparatus for localized microtransection or macrotransection of conduction paths within the heart.
It is a further object of the present invention to provide a thin, flexible catheter which can be advanced through a body vessel to perform localized thermal ablation of internal body organs.
It is still another object of the present invention to provide methods and apparatus for sensing conduction potentials within the heart and for performing localized thermal ablation of the conduction paths.
It is still another object of the present invention to provide a thin, flexible catheter having a resistive heating element at its distal end to perform localized thermal ablation.
It is a still further object of the present invention to provide a thin, flexible catheter having a prescribed shape so that a resistive heating element at the distal end contacts a desired location in a prescribed alignment therewith.